In recent years, there has been an enormous amount of laboratory activity testing ozone for bleaching cellulose pulp. Ozone is considered one of the potentially most advantageous future bleaching chemicals since it does not have the environmental drawbacks of chlorine, and reacts quickly with cellulose pulp. A number of experiments have been carried out utilizing cellulose pulp at medium consistency (i.e., about 6 to 18%) since that is a desirable consistency at which to effect bleaching if possible, and heretofore not much has been known about medium consistency ozone bleaching since conventional wisdom in the art was that it was not feasible.
According to the present invention, a method and apparatus are provided for conducting laboratory experiments treating cellulosic pulp with gas containing ozone as the primary reactive ingredient. Conventional prior laboratory apparatus, such as shown in FIG. 1 of an article by Laxen et al published in Paper and Timber at 72 (1990):5 and entitled "Medium-Consistency Ozone Bleaching" utilize an ozone pressure vessel. This vessel is a twenty-liter vessel used to store or discharge the ozone-oxygen gas mixture into the reactor/mixer. However, due to the large volume of this vessel and the inherent variation of the temperature and pressure of the gas mixture during discharge, and because a complex mathematical formula of questionable accuracy must be utilized to calculate the amount of ozone, the amount of ozone actually discharged to the reactor/mixer was difficult, if not impossible, to accurately determine utilizing this laboratory apparatus.
The method and apparatus according to the present invention overcome the drawbacks of the prior art. According to the present invention the inaccuracies present in determining the amount of ozone discharged into the reactor/mixer that were inherent in the prior art no longer exist. Also, since the ozone generator is connected to other components in such a way that it can be run continuously, problems associated with inconsistent ozone quality are also eliminated. The system according to the present invention is totally automated and computer controlled, allowing accurate yet simple practice of laboratory experiments for the ozone bleaching of pulp.
According to one aspect of the present invention, a method of conducting laboratory experiments treating cellulose pulp with gas containing ozone, using an injection cylinder and a laboratory mixer is provided. The method comprises the following steps: (a) Feeding cellulosic pulp into the mixer. (b) Charging the cylinder with a known predetermined amount of ozone containing gas. (c) Injecting the ozone containing gas from the cylinder into the mixer. (d) Mixing the ozone containing gas with the pulp in the mixer for a predetermined period of time. And (e) venting gas containing residual ozone which has not reacted with the pulp from the mixer, including by using purge gas. There is also preferably the further steps (f) of verifying the amount of ozone in the cylinder after charging but before injecting, (g) continuously creating ozone from oxygen containing gas and (h) when step (b) is not being practiced, effecting destruction of the ozone being continuously produced; and (i) determining the amount of residual ozone in the gas vented in step (e). Multiple or partial injections may also be used for the ozone charge to the mixer for a particular test.
According to another aspect of the present invention a laboratory apparatus is provided for practicing experiments mixing ozone with cellulosic pulp. The apparatus comprises the following components: An ozone generator. A cylinder housing with a movable piston, and means for moving the piston to eject gas from the housing. A mixer for mixing ozone containing gas with pulp, and having a vent. First conduit means connecting the ozone generator to the cylinder. Second conduit means connecting the cylinder housing to the mixer. First automatically operated valve means disposed in the first conduit means for selectively directing ozone from the generator to the cylinder housing. And second automatically operated valve means disposed in the second conduit means for selectively allowing or preventing ozone containing gas from passing from the cylinder housing to the mixer.
The mixer is preferably a fluidizing mixer, and the vent from the mixer is connected to an ozone destruct device through a residual ozone analyzer (such as a pair of vessels filled part way with potassium iodide solution and having the inlet to each vessel extending below the level of the potassium iodide, and the outlet extending from above the level of potassium iodide, the vessels connected in series). Control means are also provided for controlling the means for moving the piston, and the first and second automatically operated valves, for injecting a predetermined amount of ozone containing gas into the mixer at a desired time between just prior to mixer start up and to about one second after mixer start up.
According to yet another aspect of the present invention, a laboratory injection cylinder assembly is provided. This assembly comprises: A cylinder housing. A piston disposed in the housing and having a first face and a second face opposite the first face. A piston rod extending generally perpendicularly to the piston second face, exteriorly of the housing. A transducer connected to the piston rod for determining the position of the piston rod with respect to the interior of the cylinder housing. A first port disposed in the cylinder housing on a portion thereof adjacent the piston first face when the piston is disposed at a first end of the housing. A first conduit connected to the first port, and branching into second and third conduits. And first and second automatically operated valves, the first valve disposed in the second conduit, and the second valve disposed in the third conduit.
The piston preferably is of PVC or like plastic, connected by threads to the piston rod and elongated a substantial distance (e.g., almost three inches) in the dimension of the piston rod. It preferably includes first and second circumferential O-rings disposed circumferentially around the piston between the first and second faces thereof.
It is a primary object of the present invention to provide for the accurate, yet simple to perform, practice of laboratory experiments treating cellulose pulp with ozone containing gas, particularly when the pulp has a consistency of about 6-18%. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.